1. Field of the Invention
This invention relates to a rolling bearing device for supporting a pinion shaft (hereinafter referred to as “bearing device”) for rotatably supporting two portions (that is, a pinion gear-side portion and a counter-pinion-gear-side portion) of a pinion shaft (incorporated in an automotive differential apparatus, a transfer apparatus for a four-wheel drive vehicle or the like) by rolling bearings.
2. Related Art
In an automotive differential apparatus and a transfer apparatus for a four-wheel drive vehicle, it has heretofore been proposed to use a bearing device, in which tapered roller bearings (serving as rolling bearings) are provided respectively at a pinion gear-side portion (one axial end portion) of a pinion shaft and a counter-pinion-gear-side portion (the other axial end portion) of the pinion shaft, and the pinion shaft is rotatably supported on an inner periphery surface of a case by the two tapered roller bearings (see JP-A-9-105450 Publication and JP-A-10-220468 Publication).
In the above bearing device, a radial load and a thrust load simultaneously act on the pinion gear-side tapered roller bearing, and since the proportion of the thrust load is high, this tapered roller bearing has a large contact angle. Therefore, a large frictional resistance acts on this tapered roller bearing, so that a rotational torque is large.
Under the circumstances, there has been proposed a bearing device in which instead of a tapered roller bearing, a double row rolling bearing is used as a pinion gear-side rolling bearing, and this double row rolling bearing includes two axially-arranged rows of rolling elements having different pitch circle diameters (JP-A-2004-190728 Publication).
A differential apparatus, in which a pinion gear-side portion of a pinion shaft is supported on an inner peripheral surface of a case by this double row rolling bearing, will be described with reference to FIG. 7.
The differential apparatus 1 includes the case 2. The case 2 comprises a front case 3 and a rear case 4, and the two cases 3 and 4 are joined together by bolt/nut arrangements 2a.
Bearing-mounting annular walls 27A and 27B are formed within the front case 3. The case 2 contains a differential mechanism 5 connecting right and left wheels together in a differential manner, and a pinion shaft 7 having a pinion gear 6.
The pinion gear 6 is in mesh with a ring gear 8 of the differential mechanism 5.
A shaft portion 9 of the pinion shaft 7 is stepped to increase in diameter toward the pinion gear 6. A pinion gear-side portion of the shaft portion 9 of the pinion shaft 7 is rotatably supported on the annular wall 27A of the front case 3 via a double row rolling bearing 10.
A counter-pinion-gear-side portion (that is, a portion remote from the pinion gear) of the shaft portion 9 of the pinion shaft 7 is rotatably supported on the annular wall 27B of the front case 3 via a rolling bearing 25.
The front case 3 has an oil circulating passageway 40 formed between its outer wall and the annular wall 27A, and an oil inlet 41 of the oil circulating passageway 40 is open toward the ring gear 8, and an oil outlet 42 of the oil circulating passageway 40 is open to a region between the annular walls 27A and 27B.
A closure plate 37 is inserted into the front case 3 through a smaller-diameter opening thereof, and is fitted on the shaft portion 9 of the pinion shaft 7.
A barrel portion 44 of a companion flange 43 is spline-fitted on the shaft portion 9, and an end surface of this barrel portion 44 is held against the closure plate 37. An oil seal 46 is mounted on the barrel portion 44 of the companion flange 43.
A seal protection cup 47 is attached to the smaller-diameter opening portion of the front case 3.
A nut 49 is threaded on a threaded portion 48 of the shaft portion 9, thereby imparting a predetermined preload to rows 17 and 18 of rolling elements of the double row rolling bearing 10 and a row 30 of rolling elements of the rolling bearing 25.
In the above construction, the nut 49 is threaded on the threaded portion 48, so that an inner ring 13 of the double row rolling bearing 10 and an inner ring 14 of the rolling bearing 25 are clamped in the axial direction to be held between the end surface of the pinion gear 6 and the end surface of the companion flange 43, thereby imparting the predetermined preload to the rows 17 and 18 of rolling elements of the double row rolling bearing 10 and the row 30 of rolling elements of the rolling bearing 25 through the closure plate 37 and a plasticity spacer 23.
The conventional double row rolling bearing 10 will be described with reference to FIG. 8. This double row rolling bearing 10 is a double row angular contact ball bearing. This double row angular contact ball bearing includes the two axially-arranged rows of rolling elements (having different pitch circle diameters) disposed between the inner and outer rings, contact angles of the two rows of rolling elements being set in the same direction. The double row rolling bearing 10 comprises the double-raceway outer ring 11 having a larger-diameter raceway 11a and a smaller-diameter raceway 11b which are arranged axially, the double-raceway inner ring 13 having a larger-diameter raceway 13a and a smaller-diameter raceway 13b which are arranged axially, and are opposed respectively to the larger-diameter raceway 11a and the smaller-diameter raceway 11b in the radial direction, the larger-diameter row 17 of balls disposed between the larger-diameter raceways 11a and 13a, the smaller-diameter row 18 of balls disposed between the smaller-diameter raceways 11b and 13b, a larger-diameter-side cage 19 holding the larger-diameter row 17 of balls, and a smaller-diameter-side cage 20 holding the smaller-diameter row 18 of balls.
In this double row rolling bearing 10, the inclinations of the contact angles of the larger-diameter and smaller-diameter rows 17 and 18 of balls to the corresponding raceways 11a and 13a; 11b and 13b are in the same direction.
The reason why the double row rolling bearing 10 is used as the pinion gear-side bearing while the rolling bearing 25 is used as the counter-pinion-gear-side bearing is that capacities of loads (i.e., an axial load and a radial load) are larger at the pinion gear-side than at the counter-pinion-gear-side.
A problem with the double row rolling bearing 10 of the above construction will be described below.
The double row rolling bearing 10 is in the form of a double row angular contact ball bearing, and the diameters of the pitch circles of the two ball rows 17 and 18 are different from each other.
When the pinion shaft rotates about its axis, a pumping action is produced by the rotation of the inner ring 13 and the rolling motion of balls forming the ball rows 17 and 18, and oil from the oil outlet 42 of the oil circulating passageway 40 is drawn through an opening between the annular walls 27A and 27B into the interior of the double row rolling bearing 10 from the right end side (in the drawings) of this bearing, and the thus drawn oil passes through the interior of the bearing as indicated by arrows (in the drawings).
By this pumping action, an excessive amount of oil larger than the required amount for lubrication purposes passes through the bearing in the directions of the arrows, and because of this excess passing oil, an oil agitation loss in the interior of the double row rolling bearing 10 increases, and this causes a torque loss.